1. Field of the Invention
The present invention relates to a vehicular alternator failure determination apparatus, and more particularly, to the decision of failure determination conditions upon making a failure determination of a vehicular alternator.
2. Description of the Related Art
In diagnosis apparatuses for motor vehicles with known vehicular alternator failure determination means, the generation cycle or period of a ripple voltage in the output of a vehicular alternator rectifier or commutating device is measured so that a failure in a stator coil and commutator elements in the rectifier or commutating device is detected according to a variation in the ripple voltage generation cycle. Explaining this step by step, in a first step, the cycle or period of a ripple voltage waveform at a certain point in time is read in, and when the cycle thus read in is larger than zero or a predetermined value α, it is determined that the stator coil is in a failure state. In a second step, a difference between the ripple voltage waveform cycle at the certain point in time and the last (i.e., one cycle before) ripple voltage waveform cycle is calculated, and if this difference or change is equal to or greater than a predetermined value β, it is determined that the commutating device is in a failure state. In a third step, an average or mean voltage is read in, and then in a fourth step, a difference between the average or mean voltage thus read and a reference voltage is calculated, and if the difference is equal to or greater than a predetermined value γ, it is determined that a voltage regulation device is in a failure state (for instance, see Japanese patent document 1: Japanese patent laid-open No. Hei 1-25333).
As explained above, in the known vehicular alternator failure means, a small ripple voltage waveform of the voltage difference when the vehicular alternator is in a state of normal power generation is detected to calculate its cycle or period. Thus, ripple detection is carried out by removing a DC component of the vehicular alternator commutating device output. However, the vehicular alternator does not always perform power generation but irregular intermittent power generation. In addition, the number of revolutions per minute of the vehicular alternator depends on that of the engine of a vehicle. For the above-mentioned reasons, the output voltage of the vehicular alternator is varying in accordance with time, and hence, a ripple component due to a change in the operating condition of the engine can not be completely removed by removing a DC component alone. Moreover, since the influence of noise on the ripple component is also large, there is a problem that it is difficult to make a clear distinction between the ripple component due to an engine operating condition change and the ripple voltage resulting from noise or failure. Furthermore, since the output voltage of the vehicular alternator is varying in accordance with time for the reasons as stated above, there is also another problem that it is difficult to obtain an accurate average or mean value upon calculation of an average or mean output voltage of the alternator.